Letter to the Editor

Magnetars as persistent hard X-ray sources: INTEGRAL discovery of a hard tail in SGR 1900+14

¹ CEA Saclay, DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette, France e-mail: diego.gotz@cea.fr
² INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, via Bassini 15, 20133 Milano, Italy
³ Dipartimento di Fisica Nucleare e Teorica – Università degli Studi di Pavia, via Bassi 6, 27100 Pavia, Italy

Received: 17 January 2006
Accepted: 20 February 2006

Abstract

Using 2.5 Ms of data obtained by the INTEGRAL  satellite in 2003-2004, we discovered persistent hard X-ray emission from the soft gamma-ray repeater SGR 1900+14. Its 20-100 keV spectrum is well described by a steep power law with photon index and flux  erg cm^-2 s^-1. Contrary to SGR 1806–20, the only other soft gamma-ray repeater for which persistent emission above 20 keV was reported, SGR 1900+14 has been detected in the hard X-ray range while it was in a quiescent state (the last bursts from this source were observed in 2002). By comparing the broad band spectra (1-100 keV) of all the magnetars detected by INTEGRAL  (the two SGRs and three anomalous X-ray pulsars) we find evidence for a different spectral behaviour of these two classes of sources.